The overall goal of this project is to examine the mechanism of cell-cell interactions in the developing and adult mammary gland (MG) focusing specifically on Wnt genes, transforming growth factor (TGFalpha), and keratinocyte growth factor (KGF). The rationale for this project is the concept that cell-cell interactions play exceeding important roles during development of the MG and may play a permissive role during carcinogenesis. The three areas of focus (Wnt genes, growth factors are all known to be involved in cell-cell interactions or to perturb such interactions. Wnt-1, which encodes a cell surface protein involved in cell-cell interactions and mammary carcinogenesis, will be studied to determine whether its actions in vivo in the MG are due to epithelial- epithelial versus mesenchymal-epithelial interactions. An examination of the ontogeny of Wnt-1 expression in MGs of Wnt-1 transgenic mice will give clues as to types of developmental processes mediated by Wnt-1 and possibly the relationship of Wnt-1 expression to the mesenchymal- epithelial interactions that elicit androgen-induced mammary epithelial regression. The role of KGF and TGFalpha as paracrine/autocrine factors will be explored focusing specifically on fetal and early neonatal mammary development, which has received little attention by past investigators. For this purpose we will (a) examine the ontogeny of KGF and TGFalpha expression during MG development, (b) investigate the spatial distribution of the growth factors within the mammary ductal "tree" (c) examined the hormonal regulation of KGF and TGFalpha expression (d) examine the actions of KGF and TGFalpha during MG development and (e) examine KGF receptor expression. For these studies the fetal and neonatal MG will be examined since this is a period for which little is known concerning growth regulatory mechanisms in the MG. By exploiting our recently developed model of induction of mammary differentiation from skin epithelium, we will test the hypothesis that induction of mammary differentiation in epidermis by mammary mesenchyme elicits a dramatic change in the endocrine/autocrine/paracrine profile of the induced epithelium resulting in the mesenchyme-expression of TGFalpha and EGF by the epithelium. The possibility that interactions with connective tissue are involved in maintaining endocrine/autocrine/paracrine features will also be examined. To achieve these goals, the following techniques will be used, cell and organ culture, tissue recombination, in vivo grafting, immunocytochemistry, in situ hybridization, Western blot, Northern blot, RT-PCR, substrate gels, autoradiography and morphometries. It is anticipated that completion of the proposed studies will provide important insights into regulation of growth and differentiation in the MG and in mammary cancers.